Network Working Group E. Hammer-Lahav, Ed.
Internet-Draft Yahoo!
Obsoletes: 5849 (if approved) D. Recordon
Intended status: Standards Track Facebook
Expires: November 20, 2011 D. Hardt
Microsoft
May 19, 2011
The OAuth 2.0 Authorization Protocoldraft-ietf-oauth-v2-16
Abstract
The OAuth 2.0 authorization protocol enables a third-party
application to obtain limited access to an HTTP service, either on
behalf of an end-user by orchestrating an approval interaction
between the end-user and the HTTP service, or by allowing the third-
party application to obtain access on its own behalf.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on November 20, 2011.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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to this document. Code Components extracted from this document must
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Internet-Draft OAuth 2.0 May 20111. Introduction
In the traditional client-server authentication model, the client
accesses a protected resource on the server by authenticating with
the server using the resource owner's credentials. In order to
provide third-party applications access to protected resources, the
resource owner shares its credentials with the third-party. This
creates several problems and limitations:
o Third-party applications are required to store the resource-
owner's credentials for future use, typically a password in clear-
text.
o Servers are required to support password authentication, despite
the security weaknesses created by passwords.
o Third-party applications gain overly broad access to the resource-
owner's protected resources, leaving resource owners without any
ability to restrict duration or access to a limited subset of
resources.
o Resource owners cannot revoke access to an individual third-party
without revoking access to all third-parties, and must do so by
changing their password.
OAuth addresses these issues by introducing an authorization layer
and separating the role of the client from that of the resource
owner. In OAuth, the client requests access to resources controlled
by the resource owner and hosted by the resource server, and is
issued a different set of credentials than those of the resource
owner.
Instead of using the resource owner's credentials to access protected
resources, the client obtains an access token - a string denoting a
specific scope, duration, and other access attributes. Access tokens
are issued to third-party clients by an authorization server with the
approval of the resource owner. The client uses the access token to
access the protected resources hosted by the resource server.
For example, a web end-user (resource owner) can grant a printing
service (client) access to her protected photos stored at a photo
sharing service (resource server), without sharing her username and
password with the printing service. Instead, she authenticates
directly with a server trusted by the photo sharing service
(authorization server) which issues the printing service delegation-
specific credentials (access token).
This specification is designed for use with HTTP [RFC2616]. The use
of OAuth with any transport protocol other than HTTP is undefined.
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Internet-Draft OAuth 2.0 May 20111.1. Roles
OAuth includes four roles working together to grant and provide
access to protected resources - access restricted resources which
require authentication to access:
resource owner
An entity capable of granting access to a protected resource.
When the resource owner is a person, it is referred to as an end-
user.
resource server
The server hosting the protected resources, capable of accepting
and responding to protected resource requests using access tokens.
client
An application making protected resource requests on behalf of the
resource owner and with its authorization.
authorization server
The server issuing access tokens to the client after successfully
authenticating the resource owner and obtaining authorization.
The interaction between the authorization server and resource server
is beyond the scope of this specification. The authorization server
may be the same server as the resource server or a separate entity.
A single authorization server may issue access tokens accepted by
multiple resource servers.
1.2. Protocol Flow
When interacting with the authorization server, the client identifies
itself using a set of client credentials which include a client
identifier and other authentication attributes. The means through
which the client obtains its credentials are beyond the scope of this
specification, but typically involve registration with the
authorization server.
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resource owner, and enforced by the resource server and authorization
server.
The token may denote an identifier used to retrieve the authorization
information, or self-contain the authorization information in a
verifiable manner (i.e. a token string consisting of some data and a
signature). Additional authentication credentials may be required in
order for the client to use a token.
The access token provides an abstraction layer, replacing different
authorization constructs (e.g. username and password) with a single
token understood by the resource server. This abstraction enables
issuing access tokens more restrictive than the authorization grant
used to obtain them, as well as removing the resource server's need
to understand a wide range of authentication methods.
Access tokens can have different formats, structures, and methods of
utilization (e.g. cryptographic properties) based on the resource
server security requirements. Access token attributes and the
methods used to access protected resources are beyond the scope of
this specification and are defined by companion specifications.
1.4. Authorization Grant
An authorization grant is a general term used to describe the
intermediate credentials representing the resource owner
authorization (to access its protected resources), and serves as an
abstraction layer. An authorization grant is used by the client to
obtain an access token.
This specification defines four grant types: authorization code,
implicit, resource owner password credentials, and client
credentials, as well as an extensibility mechanism for defining
additional types.
1.4.1. Authorization Code
The authorization code is obtained by using an authorization server
as an intermediary between the client and resource owner. Instead of
requesting authorization directly from the resource owner, the client
directs the resource owner to an authorization server (via its user-
agent as defined in [RFC2616]), which in turn directs the resource
owner back to the client with the authorization code.
Before directing the resource owner back to the client with the
authorization code, the authorization server authenticates the
resource owner and obtains authorization. Because the resource owner
only authenticates with the authorization server, the resource
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owner's credentials are never shared with the client.
The authorization code provides a few important security benefits
such as the ability to authenticate the client and issuing the access
token directly to the client without potentially exposing it to
others, including the resource owner.
1.4.2. Implicit
When an access token is issued to the client directly as the result
of the resource owner authorization, without an intermediary
authorization grant (such as an authorization code), the grant is
considered implicit.
When issuing an implicit grant, the authorization server cannot
verify the identity of the client, and the access token may be
exposed to the resource owner or other applications with access to
the resource owner's user-agent.
Implicit grants improve the responsiveness and efficiency of some
clients (such as a client implemented as an in-browser application)
since it reduces the number of round trips required to obtain an
access token.
1.4.3. Resource Owner Password Credentials
The resource owner password credentials (e.g. a username and
password) can be used directly as an authorization grant to obtain an
access token. The credentials should only be used when there is a
high degree of trust between the resource owner and the client (e.g.
its computer operating system or a highly privileged application),
and when other authorization grant types are not available (such as
an authorization code).
Even though this grant type requires direct client access to the
resource owner credentials, the resource owner credentials are used
for a single request and are exchanged for an access token. Unlike
the HTTP Basic authentication scheme defined in [RFC2617], this grant
type (when combined with a refresh token) eliminates the need for the
client to store the resource-owner credentials for future use.
1.4.4. Client Credentials
The client credentials can be used as an authorization grant when the
authorization scope is limited to the protected resources under the
control of the client, or to protected resources previously arranged
with the authorization server. Client credentials are used as an
authorization grant typically when the client is acting on its own
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behalf (the client is also the resource owner).
1.4.5. Extensions
Additional grant types may be defined to provide a bridge between
OAuth and other protocols. For example,
[I-D.ietf-oauth-saml2-bearer] defines a SAML 2.0
[OASIS.saml-core-2.0-os] bearer assertion grant type, which can be
used to obtain an access token.
1.5. Refresh Token
A refresh token is optionally issued by the authorization server to
the client together with an access token. The client can use the
refresh token to request another access token based on the same
authorization, without having to involve the resource owner again, or
having to retain the original authorization grant used to obtain the
initial access token.
A refresh token is a string representing the authorization granted to
the client by the resource owner. The string is usually opaque to
the client. The token may denote an identifier used to retrieve the
authorization information, or self-contain the authorization
information in a verifiable manner. The refresh token is bound to
the client it was issued to, and its usage requires client
authentication.
The refresh token can be used to obtain a new access token when the
current access token expires (access tokens may have a shorter
lifetime than authorized by the resource owner), no longer valid, or
to obtain additional access tokens with identical or narrower scope.
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(H) The authorization server validates the client credentials and
the refresh token, and if valid issues a new access token (and
optionally, a new refresh token).
1.6. Document Structure
This specification is organized into the following sections:
o Section 2 - describes the two endpoints used to obtain and utilize
the various authorization grant types.
o Section 3 - describes client identification and authentication in
general, and provides one such method for client authentication
using password credentials.
o Section 4 - describes the complete flow for each authorization
grant type, including requesting authorization, authorization
response, and requesting an access token.
o Section 5 - describes the common access token response used for
all non-implicit authorization grant types.
o Section 6 - describes the use of a refresh token to obtain
additional access tokens using the same resource owner
authorization.
o Section 7 - describes how access tokens are used to access
protected resources.
o Section 8 - describes how to extend certain elements of the
protocol.
o Section 9 - provides a security analysis of the protocol.
1.7. Notational Conventions
The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL NOT',
'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'MAY', and 'OPTIONAL' in this
specification are to be interpreted as described in [RFC2119].
This specification uses the Augmented Backus-Naur Form (ABNF)
notation of [RFC5234].
Unless otherwise noted, all the protocol parameter names and values
are case sensitive.
2. Protocol Endpoints
The authorization process utilizes two endpoints (HTTP resources):
o Authorization endpoint - used to obtain authorization from the
resource owner via user-agent redirection.
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o Token endpoint - used to exchange an authorization grant for an
access token, typically with client authentication.
Not every authorization grant type utilizes both endpoints.
Extension grant types MAY define additional endpoints as needed.
2.1. Authorization Endpoint
The authorization endpoint is used to interact with the resource
owner and obtain authorization which is expressed explicitly as an
authorization code (exchanged for an access token), or implicitly by
direct issuance of an access token.
The authorization server MUST first verify the identity of the
resource owner. The way in which the authorization server
authenticates the resource owner (e.g. username and password login,
session cookies) is beyond the scope of this specification.
The means through which the client obtains the location of the
authorization endpoint are beyond the scope of this specification but
is typically provided in the service documentation. The endpoint URI
MAY include a query component as defined by [RFC3986] section 3,
which MUST be retained when adding additional query parameters.
Since requests to the authorization endpoint result in user
authentication and the transmission of clear-text credentials (in the
HTTP response), the authorization server MUST require the use of a
transport-layer security mechanism when sending requests to the
authorization endpoint. The authorization server MUST support TLS
1.2 as defined in [RFC5246], and MAY support additional transport-
layer mechanisms meeting its security requirements.
The authorization server MUST support the use of the HTTP "GET"
method [RFC2616] for the authorization endpoint, and MAY support the
use of the "POST" method as well.
The REQUIRED "response_type" request parameter is used to identify
which grant type the client is requesting: authorization code or
implicit, described in Section 4.1.1 and Section 4.2.1 respectively.
If the request is missing the "response_type" parameter, the
authorization server SHOULD return an error response as described in
Section 4.1.2.1.
Parameters sent without a value MUST be treated as if they were
omitted from the request. The authorization server SHOULD ignore
unrecognized request parameters.
Request and response parameters MUST NOT repeat more than once,
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unless noted otherwise.
2.1.1. Redirection URI
The client directs the resource owner's user-agent to the
authorization endpoint and includes a redirection URI to which the
authorization server will redirect the user-agent back once
authorization has been obtained (or denied). The client MAY omit the
redirection URI if one has been established between the client and
authorization server via other means, such as during the client
registration process.
The redirection URI MUST be an absolute URI and MAY include a query
component, which MUST be retained by the authorization server when
adding additional query parameters.
The authorization server SHOULD require the client to pre-register
their redirection URI or at least certain components such as the
scheme, host, port and path. If a redirection URI was registered,
the authorization server MUST compare any redirection URI received at
the authorization endpoint with the registered URI.
The authorization server SHOULD NOT redirect the user-agent to
unregistered or untrusted URIs to prevent the endpoint from being
used as an open redirector. If no valid redirection URI is
available, the authorization server SHOULD inform the resource owner
directly of the error.
2.2. Token Endpoint
The token endpoint is used by the client to obtain an access token by
authenticating with the authorization server and presenting its
authorization grant or refresh token. The token endpoint is used
with every authorization grant except for the implicit grant type
(since an access token is issued directly).
The means through which the client obtains the location of the token
endpoint are beyond the scope of this specification but is typically
provided in the service documentation. The endpoint URI MAY include
a query component, which MUST be retained when adding additional
query parameters.
Since requests to the token endpoint result in the transmission of
clear-text credentials (in the HTTP request and response), the
authorization server MUST require the use of a transport-layer
security mechanism when sending requests to the token endpoint. The
authorization server MUST support TLS 1.2 as defined in [RFC5246],
and MAY support additional transport-layer mechanisms meeting its
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security requirements.
The token endpoint requires client authentication as described in
Section 3. The authorization server MAY accept any form of client
authentication meeting its security requirements. The client MUST
NOT use more than one authentication method in each request.
The client MUST use the HTTP "POST" method when making access token
requests.
Parameters sent without a value MUST be treated as if they were
omitted from the request. The authorization server SHOULD ignore
unrecognized request parameters.
Request and response parameters MUST NOT repeat more than once,
unless noted otherwise.
3. Client Authentication
Client credentials are used to identify and authenticate the client.
The client credentials include a client identifier - a unique string
issued to the client to identify itself to the authorization server.
The client identifier is not a secret, it is exposed to the resource
owner, and MUST NOT be used alone for client authentication. Client
authentication is accomplished via additional means such as a
matching client password.
The methods through which the client obtains its client credentials
are beyond the scope of this specification. However, the client
registration process typically includes gathering relevant
information which is used to educate the resource owner about the
client when requesting authorization.
Due to the nature of some clients, the authorization server should
not make assumptions about the confidentiality of client credentials
without establishing trust with the client. The authorization server
SHOULD NOT issue client credentials to clients incapable of keeping
their credentials confidential (typically determined during the
client registration process).
In addition, the authorization server MAY allow unauthenticated
access token requests when the client identity does not matter (e.g.
anonymous client) or when the client identity is established via
other means. For readability purposes only, this specification is
written under the assumption that the authorization server requires
some form of client authentication. However, such language does not
affect the authorization server's discretion in allowing
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unauthenticated client requests.
3.1. Client Password Authentication
[[ Pending Consensus ]]
Clients in possession of client password credentials (the client
identifier together with a shared symmetric secret) MAY use the HTTP
Basic authentication scheme as defined in [RFC2617] to authenticate
with the authorization server. The client identifier is used as the
username, and the secret is used as the password.
When using the HTTP Basic authentication scheme, the client
identifier is included twice in the request (in the "Authorization"
header and in the "client_id" parameter). The authorization server
MUST ensure the two identifiers belong to the same client.
For example (extra line breaks are for display purposes only):
POST /token HTTP/1.1
Host: server.example.com
Authorization: Basic czZCaGRSa3F0MzpnWDFmQmF0M2JW
Content-Type: application/x-www-form-urlencoded
grant_type=authorization_code&client_id=s6BhdRkqt3&
code=i1WsRn1uB1&
redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb
Alternatively, the authorization server MAY allow including the
client secret in the request body using the following parameter:
client_secret
REQUIRED. The client secret.
The use of the "client_secret" parameter is NOT RECOMMENDED, and
should be limited to clients unable to directly utilize the HTTP
Basic authentication scheme.
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For example (extra line breaks are for display purposes only):
POST /token HTTP/1.1
Host: server.example.com
Content-Type: application/x-www-form-urlencoded
grant_type=authorization_code&client_id=s6BhdRkqt3&
client_secret=gX1fBat3bV&code=i1WsRn1uB1&
redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb
Since requests using this authentication method result in the
transmission of clear-text credentials, the authorization server MUST
require the use of a transport-layer security mechanism when sending
requests to the token endpoint.
3.2. Other Client Authentication Methods
The authorization server MAY support any suitable HTTP authentication
scheme matching its security requirements. When using other
authentication methods, the authorization server MUST define a
mapping between the client identifier and the credentials used to
authenticate.
4. Obtaining Authorization
To request an access token, the client obtains authorization from the
resource owner. The authorization is expressed in the form of an
authorization grant which the client uses to request the access
token. OAuth defines four grant types: authorization code, implicit,
resource owner password credentials, and client credentials. It also
provides an extension mechanism for defining additional grant types.
4.1. Authorization Code
The authorization code grant type is suitable for clients capable of
maintaining their client credentials confidential (for authenticating
with the authorization server) such as a client implemented on a
secure server. As a redirection-based flow, the client must be
capable of interacting with the resource owner's user-agent
(typically a web browser) and capable of receiving incoming requests
(via redirection) from the authorization server.
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(D) The client requests an access token from the authorization
server's token endpoint by authenticating using its client
credentials, and includes the authorization code received in the
previous step. The client includes the redirection URI used to
obtain the authorization code for verification.
(E) The authorization server validates the client credentials, the
authorization code, and ensures the redirection URI received
matches the URI used to redirect the client in step (C). If
valid, responds back with an access token.
4.1.1. Authorization Request
The client constructs the request URI by adding the following
parameters to the query component of the authorization endpoint URI
using the "application/x-www-form-urlencoded" format as defined by
[W3C.REC-html401-19991224]:
response_type
REQUIRED. Value MUST be set to "code".
client_id
REQUIRED. The client identifier as described in Section 3.
redirect_uri
REQUIRED, unless a redirection URI has been established between
the client and authorization server via other means. Described
in Section 2.1.1.
scope
OPTIONAL. The scope of the access request expressed as a list
of space-delimited, case sensitive strings. The value is
defined by the authorization server. If the value contains
multiple space-delimited strings, their order does not matter,
and each string adds an additional access range to the
requested scope.
state
OPTIONAL. An opaque value used by the client to maintain state
between the request and callback. The authorization server
includes this value when redirecting the user-agent back to the
client.
The client directs the resource owner to the constructed URI using an
HTTP redirection response, or by other means available to it via the
user-agent.
For example, the client directs the user-agent to make the following
HTTP request using transport-layer security (extra line breaks are
for display purposes only):
GET /authorize?response_type=code&client_id=s6BhdRkqt3&
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redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb HTTP/1.1
Host: server.example.com
The authorization server validates the request to ensure all required
parameters are present and valid. If the request is valid, the
authorization server authenticates the resource owner and obtains an
authorization decision (by asking the resource owner or by
establishing approval via other means).
When a decision is established, the authorization server directs the
user-agent to the provided client redirection URI using an HTTP
redirection response, or by other means available to it via the user-
agent.
4.1.2. Authorization Response
If the resource owner grants the access request, the authorization
server issues an authorization code and delivers it to the client by
adding the following parameters to the query component of the
redirection URI using the "application/x-www-form-urlencoded" format:
code
REQUIRED. The authorization code generated by the
authorization server. The authorization code SHOULD expire
shortly after it is issued to minimize the risk of leaks. The
client MUST NOT reuse the authorization code. If an
authorization code is used more than once, the authorization
server MAY revoke all tokens previously issued based on that
authorization code. The authorization code is bound to the
client identifier and redirection URI.
state
REQUIRED if the "state" parameter was present in the client
authorization request. Set to the exact value received from
the client.
For example, the authorization server redirects the user-agent by
sending the following HTTP response:
HTTP/1.1 302 Found
Location: https://client.example.com/cb?code=i1WsRn1uB1
The client SHOULD ignore unrecognized response parameters. The
authorization code string size is left undefined by this
specification. The client should avoid making assumptions about code
value sizes. The authorization server should document the size of
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any value it issues.
4.1.2.1. Error Response
If the request fails due to a missing, invalid, or mismatching
redirection URI, or if the client identifier provided is invalid, the
authorization server SHOULD inform the resource owner of the error,
and MUST NOT redirect the user-agent to the invalid redirection URI.
If the resource owner denies the access request or if the request
fails for reasons other than a missing or invalid redirection URI,
the authorization server informs the client by adding the following
parameters to the query component of the redirection URI using the
"application/x-www-form-urlencoded" format:
error
REQUIRED. A single error code from the following:
invalid_request
The request is missing a required parameter, includes an
unsupported parameter or parameter value, or is otherwise
malformed.
unauthorized_client
The client is not authorized to request an authorization
code using this method.
access_denied
The resource owner or authorization server denied the
request.
unsupported_response_type
The authorization server does not support obtaining an
authorization code using this method.
invalid_scope
The requested scope is invalid, unknown, or malformed.
a 4xx or 5xx HTTP status code (except for 400 and 401)
The authorization server MAY set the "error" parameter
value to a numerical HTTP status code from the 4xx or 5xx
range, with the exception of the 400 (Bad Request) and
401 (Unauthorized) status codes. For example, if the
service is temporarily unavailable, the authorization
server MAY return an error response with "error" set to
"503".
error_description
OPTIONAL. A human-readable text providing additional
information, used to assist in the understanding and resolution
of the error occurred. [[ add language and encoding information
]]
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error_uri
OPTIONAL. A URI identifying a human-readable web page with
information about the error, used to provide the resource owner
with additional information about the error.
state
REQUIRED if a valid "state" parameter was present in the client
authorization request. Set to the exact value received from
the client.
For example, the authorization server redirects the user-agent by
sending the following HTTP response:
HTTP/1.1 302 Found
Location: https://client.example.com/cb?error=access_denied
4.1.3. Access Token Request
The client makes a request to the token endpoint by adding the
following parameters using the "application/x-www-form-urlencoded"
format in the HTTP request entity-body:
grant_type
REQUIRED. Value MUST be set to "authorization_code".
client_id
REQUIRED. The client identifier as described in Section 3.
code
REQUIRED. The authorization code received from the
authorization server.
redirect_uri
REQUIRED. The redirection URI used by the authorization server
to return the authorization response in the previous step.
The client includes its authentication credentials as described in
Section 3
For example, the client makes the following HTTP using transport-
layer security (extra line breaks are for display purposes only):
POST /token HTTP/1.1
Host: server.example.com
Authorization: Basic czZCaGRSa3F0MzpnWDFmQmF0M2JW
Content-Type: application/x-www-form-urlencoded
grant_type=authorization_code&client_id=s6BhdRkqt3&
code=i1WsRn1uB1&
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redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb
The authorization server MUST:
o Validate the client credentials and ensure that the authorization
code was issued to that client.
o Verify that the authorization code is valid, and that the
redirection URI matches the redirection URI used by the
authorization server to deliver the authorization code.
4.1.4. Access Token Response
If the access token request is valid and authorized, the
authorization server issues an access token and optional refresh
token as described in Section 5.1. If the request client
authentication failed or is invalid, the authorization server returns
an error response as described in Section 5.2.
An example successful response:
HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
{
"access_token":"SlAV32hkKG",
"token_type":"example",
"expires_in":3600,
"refresh_token":"8xLOxBtZp8",
"example_parameter":"example_value"
}
4.2. Implicit Grant
The implicit grant type is suitable for clients incapable of
maintaining their client credentials confidential (for authenticating
with the authorization server) such as client applications residing
in a user-agent, typically implemented in a browser using a scripting
language such as JavaScript.
As a redirection-based flow, the client must be capable of
interacting with the resource owner's user-agent (typically a web
browser) and capable of receiving incoming requests (via redirection)
from the authorization server.
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The flow illustrated in Figure 4 includes the following steps:
(A) The client initiates the flow by directing the resource owner's
user-agent to the authorization endpoint. The client includes
its client identifier, requested scope, local state, and a
redirection URI to which the authorization server will send the
user-agent back once access is granted (or denied).
(B) The authorization server authenticates the resource owner (via
the user-agent) and establishes whether the resource owner
grants or denies the client's access request.
(C) Assuming the resource owner grants access, the authorization
server redirects the user-agent back to the client using the
redirection URI provided earlier. The redirection URI includes
the access token in the URI fragment.
(D) The user-agent follows the redirection instructions by making a
request to the web server (does not include the fragment). The
user-agent retains the fragment information locally.
(E) The web server returns a web page (typically an HTML document
with an embedded script) capable of accessing the full
redirection URI including the fragment retained by the user-
agent, and extracting the access token (and other parameters)
contained in the fragment.
(F) The user-agent executes the script provided by the web server
locally, which extracts the access token and passes it to the
client.
4.2.1. Authorization Request
The client constructs the request URI by adding the following
parameters to the query component of the authorization endpoint URI
using the "application/x-www-form-urlencoded" format:
response_type
REQUIRED. Value MUST be set to "token".
client_id
REQUIRED. The client identifier as described in Section 3.
redirect_uri
REQUIRED, unless a redirection URI has been established between
the client and authorization server via other means. Described
in Section 2.1.1.
scope
OPTIONAL. The scope of the access request expressed as a list
of space-delimited, case sensitive strings. The value is
defined by the authorization server. If the value contains
multiple space-delimited strings, their order does not matter,
and each string adds an additional access range to the
requested scope.
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state
OPTIONAL. An opaque value used by the client to maintain state
between the request and callback. The authorization server
includes this value when redirecting the user-agent back to the
client.
The client directs the resource owner to the constructed URI using an
HTTP redirection response, or by other means available to it via the
user-agent.
For example, the client directs the user-agent to make the following
HTTP request using transport-layer security (extra line breaks are
for display purposes only):
GET /authorize?response_type=token&client_id=s6BhdRkqt3&
redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb HTTP/1.1
Host: server.example.com
The authorization server validates the request to ensure all required
parameters are present and valid. If the request is valid, the
authorization server authenticates the resource owner and obtains an
authorization decision (by asking the resource owner or by
establishing approval via other means).
When a decision is established, the authorization server directs the
user-agent to the provided client redirection URI using an HTTP
redirection response, or by other means available to it via the user-
agent.
4.2.2. Access Token Response
If the resource owner grants the access request, the authorization
server issues an access token and delivers it to the client by adding
the following parameters to the fragment component of the redirection
URI using the "application/x-www-form-urlencoded" format:
access_token
REQUIRED. The access token issued by the authorization server.
token_type
REQUIRED. The type of the token issued as described in
Section 7.1. Value is case insensitive.
expires_in
OPTIONAL. The duration in seconds of the access token
lifetime. For example, the value "3600" denotes that the
access token will expire in one hour from the time the response
was generated.
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scope
OPTIONAL. The scope of the access request expressed as a list
of space-delimited, case sensitive strings. The value is
defined by the authorization server. If the value contains
multiple space-delimited strings, their order does not matter,
and each string adds an additional access range to the
requested scope. The authorization server SHOULD include the
parameter if the requested scope is different from the one
requested by the client.
state
REQUIRED if the "state" parameter was present in the client
authorization request. Set to the exact value received from
the client.
For example, the authorization server redirects the user-agent by
sending the following HTTP response (URI extra line breaks are for
display purposes only):
HTTP/1.1 302 Found
Location: http://example.com/rd#access_token=FJQbwq9&
token_type=example&expires_in=3600
The client SHOULD ignore unrecognized response parameters. The
access token string size is left undefined by this specification.
The client should avoid making assumptions about value sizes. The
authorization server should document the size of any value it issues.
4.2.2.1. Error Response
If the request fails due to a missing, invalid, or mismatching
redirection URI, or if the client identifier provided is invalid, the
authorization server SHOULD inform the resource owner of the error,
and MUST NOT redirect the user-agent to the invalid redirection URI.
If the resource owner denies the access request or if the request
fails for reasons other than a missing or invalid redirection URI,
the authorization server informs the client by adding the following
parameters to the fragment component of the redirection URI using the
"application/x-www-form-urlencoded" format:
error
REQUIRED. A single error code from the following:
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invalid_request
The request is missing a required parameter, includes an
unsupported parameter or parameter value, or is otherwise
malformed.
unauthorized_client
The client is not authorized to request an access token
using this method.
access_denied
The resource owner or authorization server denied the
request.
unsupported_response_type
The authorization server does not support obtaining an
access token using this method.
invalid_scope
The requested scope is invalid, unknown, or malformed.
a 4xx or 5xx HTTP status code (except for 400 and 401)
The authorization server MAY set the "error" parameter
value to a numerical HTTP status code from the 4xx or 5xx
range, with the exception of the 400 (Bad Request) and
401 (Unauthorized) status codes. For example, if the
service is temporarily unavailable, the authorization
server MAY return an error response with "error" set to
"503".
error_description
OPTIONAL. A human-readable text providing additional
information, used to assist in the understanding and resolution
of the error occurred. [[ add language and encoding information
]]
error_uri
OPTIONAL. A URI identifying a human-readable web page with
information about the error, used to provide the resource owner
with additional information about the error.
state
REQUIRED if a valid "state" parameter was present in the client
authorization request. Set to the exact value received from
the client.
For example, the authorization server redirects the user-agent by
sending the following HTTP response:
HTTP/1.1 302 Found
Location: https://client.example.com/cb#error=access_denied
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Internet-Draft OAuth 2.0 May 20114.3. Resource Owner Password Credentials
The resource owner password credentials grant type is suitable in
cases where the resource owner has a trust relationship with the
client, such as its computer operating system or a highly privileged
application. The authorization server should take special care when
enabling the grant type, and only when other flows are not viable.
The grant type is suitable for clients capable of obtaining the
resource owner credentials (username and password, typically using an
interactive form). It is also used to migrate existing clients using
direct authentication schemes such as HTTP Basic or Digest
authentication to OAuth by converting the stored credentials with an
access token.
+----------+
| Resource |
| Owner |
| |
+----------+
v
|
(A) Password Credentials
|
v
+---------+ +---------------+
| | Client Credentials | |
| |>--(B)---- & Resource Owner ----->| |
| Client | Password Credentials | Authorization |
| | | Server |
| |<--(C)---- Access Token ---------<| |
| | (w/ Optional Refresh Token) | |
+---------+ +---------------+
Figure 5: Resource Owner Password Credentials Flow
The flow illustrated in Figure 5 includes the following steps:
(A) The resource owner provides the client with its username and
password.
(B) The client requests an access token from the authorization
server's token endpoint by authenticating using its client
credentials, and includes the credentials received from the
resource owner.
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(C) The authorization server validates the resource owner
credentials and the client credentials and issues an access
token.
4.3.1. Authorization Request and Response
The method through which the client obtains the resource owner
credentials is beyond the scope of this specification. The client
MUST discard the credentials once an access token has been obtained.
4.3.2. Access Token Request
The client makes a request to the token endpoint by adding the
following parameters using the "application/x-www-form-urlencoded"
format in the HTTP request entity-body:
grant_type
REQUIRED. Value MUST be set to "password".
client_id
REQUIRED. The client identifier as described in Section 3.
username
REQUIRED. The resource owner username, encoded as UTF-8.
password
REQUIRED. The resource owner password, encoded as UTF-8.
scope
OPTIONAL. The scope of the access request expressed as a list
of space-delimited, case sensitive strings. The value is
defined by the authorization server. If the value contains
multiple space-delimited strings, their order does not matter,
and each string adds an additional access range to the
requested scope.
The client includes its authentication credentials as described in
Section 3
For example, the client makes the following HTTP request using
transport-layer security (extra line breaks are for display purposes
only):
POST /token HTTP/1.1
Host: server.example.com
Authorization: Basic czZCaGRSa3F0MzpnWDFmQmF0M2JW
Content-Type: application/x-www-form-urlencoded
grant_type=password&client_id=s6BhdRkqt3&
username=johndoe&password=A3ddj3w
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The flow illustrated in Figure 6 includes the following steps:
(A) The client requests an access token from the token endpoint by
authenticating using its client credentials.
(B) The authorization server validates the client credentials and
issues an access token.
4.4.1. Authorization Request and Response
Since the client credentials are used as the authorization grant, no
additional authorization request is needed as the client is already
in the possession of its client credentials.
4.4.2. Access Token Request
The client makes a request to the token endpoint by adding the
following parameters using the "application/x-www-form-urlencoded"
format in the HTTP request entity-body:
grant_type
REQUIRED. Value MUST be set to "client_credentials".
client_id
REQUIRED. The client identifier as described in Section 3.
scope
OPTIONAL. The scope of the access request expressed as a list
of space-delimited, case sensitive strings. The value is
defined by the authorization server. If the value contains
multiple space-delimited strings, their order does not matter,
and each string adds an additional access range to the
requested scope.
The client includes its authentication credentials as described in
Section 3
For example, the client makes the following HTTP request using
transport-layer security (extra line breaks are for display purposes
only):
POST /token HTTP/1.1
Host: server.example.com
Authorization: Basic czZCaGRSa3F0MzpnWDFmQmF0M2JW
Content-Type: application/x-www-form-urlencoded
grant_type=client_credentials&client_id=s6BhdRkqt3
The authorization server MUST validate the client credentials.
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Internet-Draft OAuth 2.0 May 20114.4.3. Access Token Response
If the access token request is valid and authorized, the
authorization server issues an access token and optional refresh
token as described in Section 5.1. If the request failed client
authentication or is invalid, the authorization server returns an
error response as described in Section 5.2.
An example successful response:
HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
{
"access_token":"SlAV32hkKG",
"token_type":"example",
"expires_in":3600,
"refresh_token":"8xLOxBtZp8",
"example_parameter":"example_value"
}
4.5. Extensions
The client uses an extension grant type by specifying the grant type
using an absolute URI (defined by the authorization server) as the
value of the "grant_type" parameter of the token endpoint, and by
adding any additional parameters necessary.
For example, to request an access token using a SAML 2.0 assertion
grant type as defined by [I-D.ietf-oauth-saml2-bearer], the client
makes the following HTTP request using transport-layer security (line
breaks are for display purposes only):
POST /token HTTP/1.1
Host: server.example.com
Content-Type: application/x-www-form-urlencoded
grant_type=http%3A%2F%2Foauth.net%2Fgrant_type%2Fassertion%2F
saml%2F2.0%2Fbearer&assertion=PEFzc2VydGlvbiBJc3N1ZUluc3RhbnQ
[...omitted for brevity...]V0aG5TdGF0ZW1lbnQ-PC9Bc3NlcnRpb24-
If the access token request is valid and authorized, the
authorization server issues an access token and optional refresh
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token as described in Section 5.1. If the request failed client
authentication or is invalid, the authorization server returns an
error response as described in Section 5.2.
5. Issuing an Access Token
If the access token request is valid and authorized, the
authorization server issues an access token and optional refresh
token as described in Section 5.1. If the request failed client
authentication or is invalid, the authorization server returns an
error response as described in Section 5.2.
5.1. Successful Response
The authorization server issues an access token and optional refresh
token, and constructs the response by adding the following parameters
to the entity body of the HTTP response with a 200 (OK) status code:
access_token
REQUIRED. The access token issued by the authorization server.
token_type
REQUIRED. The type of the token issued as described in
Section 7.1. Value is case insensitive.
expires_in
OPTIONAL. The duration in seconds of the access token
lifetime. For example, the value "3600" denotes that the
access token will expire in one hour from the time the response
was generated.
refresh_token
OPTIONAL. The refresh token which can be used to obtain new
access tokens using the same authorization grant as described
in Section 6.
scope
OPTIONAL. The scope of the access request expressed as a list
of space-delimited, case sensitive strings. The value is
defined by the authorization server. If the value contains
multiple space-delimited strings, their order does not matter,
and each string adds an additional access range to the
requested scope. The authorization server SHOULD include the
parameter if the requested scope is different from the one
requested by the client.
The parameters are included in the entity body of the HTTP response
using the "application/json" media type as defined by [RFC4627]. The
parameters are serialized into a JSON structure by adding each
parameter at the highest structure level. Parameter names and string
values are included as JSON strings. Numerical values are included
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as JSON numbers.
The authorization server MUST include the HTTP "Cache-Control"
response header field [RFC2616] with a value of "no-store" in any
response containing tokens, secrets, or other sensitive information.
For example:
HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
{
"access_token":"SlAV32hkKG",
"token_type":"example",
"expires_in":3600,
"refresh_token":"8xLOxBtZp8",
"example_parameter":"example_value"
}
The client SHOULD ignore unrecognized response parameters. The sizes
of tokens and other values received from the authorization server are
left undefined. The client should avoid making assumptions about
value sizes. The authorization server should document the size of
any value it issues.
5.2. Error Response
The authorization server responds with an HTTP 400 (Bad Request)
status code and includes the following parameters with the response:
error
REQUIRED. A single error code from the following:
invalid_request
The request is missing a required parameter, includes an
unsupported parameter or parameter value, repeats a
parameter, includes multiple credentials, utilizes more
than one mechanism for authenticating the client, or is
otherwise malformed.
invalid_client
Client authentication failed (e.g. unknown client, no
client credentials included, multiple client credentials
included, or unsupported credentials type). The
authorization server MAY return an HTTP 401
(Unauthorized) status code to indicate which HTTP
authentication schemes are supported. If the client
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attempted to authenticate via the "Authorization" request
header field, the authorization server MUST respond with
an HTTP 401 (Unauthorized) status code, and include the
"WWW-Authenticate" response header field matching the
authentication scheme used by the client.
invalid_grant
The provided authorization grant is invalid, expired,
revoked, does not match the redirection URI used in the
authorization request, or was issued to another client.
unauthorized_client
The authenticated client is not authorized to use this
authorization grant type.
unsupported_grant_type
The authorization grant type is not supported by the
authorization server.
invalid_scope
The requested scope is invalid, unknown, malformed, or
exceeds the scope granted by the resource owner.
error_description
OPTIONAL. A human-readable text providing additional
information, used to assist in the understanding and resolution
of the error occurred. [[ add language and encoding information
]]
error_uri
OPTIONAL. A URI identifying a human-readable web page with
information about the error, used to provide the resource owner
with additional information about the error.
The parameters are included in the entity body of the HTTP response
using the "application/json" media type as defined by [RFC4627]. The
parameters are serialized into a JSON structure by adding each
parameter at the highest structure level. Parameter names and string
values are included as JSON strings. Numerical values are included
as JSON numbers.
For example:
HTTP/1.1 400 Bad Request
Content-Type: application/json
Cache-Control: no-store
{
"error":"invalid_request"
}
If the authorization server encounters an error condition other than
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the 400 (Bad Request) and 401 (Unauthorized) responses described
above (e.g. the service is temporarily unavailable), the
authorization server SHOULD include an error response in the entity
body, and set the "error" parameter value to the numerical HTTP
status code returned.
For example:
HTTP/1.1 503 Service Unavailable
Content-Type: application/json
{
"error":"503"
}
6. Refreshing an Access Token
If the authorization server issued a refresh token to the client, the
client makes a refresh request to the token endpoint by adding the
following parameters using the "application/x-www-form-urlencoded"
format in the HTTP request entity-body:
grant_type
REQUIRED. Value MUST be set to "refresh_token".
client_id
REQUIRED. The client identifier as described in Section 3.
refresh_token
REQUIRED. The refresh token issued to the client.
scope
OPTIONAL. The scope of the access request expressed as a list
of space-delimited, case sensitive strings. The value is
defined by the authorization server. If the value contains
multiple space-delimited strings, their order does not matter,
and each string adds an additional access range to the
requested scope. The requested scope MUST be equal or lesser
than the scope originally granted by the resource owner, and if
omitted is treated as equal to the scope originally granted by
the resource owner.
The client includes its authentication credentials as described in
Section 3.
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For example, the client makes the following HTTP request using
transport-layer security (extra line breaks are for display purposes
only):
POST /token HTTP/1.1
Host: server.example.com
Authorization: Basic czZCaGRSa3F0MzpnWDFmQmF0M2JW
Content-Type: application/x-www-form-urlencoded
grant_type=refresh_token&client_id=s6BhdRkqt3&
refresh_token=n4E9O119d
The authorization server MUST validate the client credentials, ensure
that the refresh token was issued to the authenticated client,
validate the refresh token, and verify that the resource owner's
authorization is still valid. If valid and authorized, the
authorization server issues an access token as described in
Section 5.1. If the request failed verification or is invalid, the
authorization server returns an error response as described in
Section 5.2.
The authorization server MAY issue a new refresh token, in which
case, the client MUST discard the old refresh token and replace it
with the new refresh token.
7. Accessing Protected Resources
The client accesses protected resources by presenting the access
token to the resource server. The resource server MUST validate the
access token and ensure it has not expired and that its scope covers
the requested resource. The methods used by the resource server to
validate the access token (as well as any error responses) are beyond
the scope of this specification, but generally involve an interaction
or coordination between the resource server and the authorization
server.
The method in which the client utilized the access token to
authenticate with the resource server depends on the type of access
token issued by the authorization server. Typically, it involves
using the HTTP "Authorization" request header field [RFC2617] with an
authentication scheme defined by the access token type specification.
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The access token type provides the client with the information
required to successfully utilize the access token to make a protected
resource request (along with type-specific attributes). The client
MUST NOT use an access token if it does not understand the token
type.
For example, the "bearer" token type defined in
[I-D.ietf-oauth-v2-bearer] is utilized by simply including the access
token string in the request:
GET /resource/1 HTTP/1.1
Host: example.com
Authorization: Bearer 7Fjfp0ZBr1KtDRbnfVdmIw
while the "mac" token type defined in [I-D.ietf-oauth-v2-http-mac] is
utilized by issuing a MAC key together with the access token which is
used to sign certain components of the HTTP requests:
GET /resource/1 HTTP/1.1
Host: example.com
Authorization: MAC id="h480djs93hd8",
nonce="274312:dj83hs9s",
mac="kDZvddkndxvhGRXZhvuDjEWhGeE="
The above examples are provided for illustration purposes only.
Developers are advised to consult the [I-D.ietf-oauth-v2-bearer] and
[I-D.ietf-oauth-v2-http-mac] specifications before use.
Each access token type definition specifies the additional attributes
(if any) sent to the client together with the "access_token" response
parameter. It also defines the HTTP authentication method used to
include the access token when making a protected resource request.
8. Extensibility8.1. Defining Access Token Types
Access token types can be defined in one of two ways: registered in
the access token type registry (following the procedures in
Section 11.1), or use a unique absolute URI as its name.
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Types utilizing a URI name SHOULD be limited to vendor-specific
implementations that are not commonly applicable, and are specific to
the implementation details of the resource server where they are
used.
All other types MUST be registered. Type names MUST conform to the
type-name ABNF. If the type definition includes a new HTTP
authentication scheme, the type name SHOULD be identical to the HTTP
authentication scheme name (as defined by [RFC2617]).
type-name = 1*name-char
name-char = "-" / "." / "_" / DIGIT / ALPHA
8.2. Defining New Endpoint Parameters
New request or response parameters for use with the authorization
endpoint or the token endpoint are defined and registered in the
parameters registry following the procedure in Section 11.2.
Parameter names MUST conform to the param-name ABNF and parameter
values syntax MUST be well-defined (e.g., using ABNF, or a reference
to the syntax of an existing parameter).
param-name = 1*name-char
name-char = "-" / "." / "_" / DIGIT / ALPHA
Unregistered vendor-specific parameter extensions that are not
commonly applicable, and are specific to the implementation details
of the authorization server where they are used SHOULD utilize a
vendor-specific prefix that is not likely to conflict with other
registered values (e.g. begin with 'companyname_').
8.3. Defining New Authorization Grant Types
New authorization grant types can be defined by assigning them a
unique absolute URI for use with the "grant_type" parameter. If the
extension grant type requires additional token endpoint parameters,
they MUST be registered in the OAuth parameters registry as described
by Section 11.2.
8.4. Defining Additional Error Codes
In cases where protocol extensions (i.e. access token types,
extension parameters, or extension grant types) require additional
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error codes to be used with the authorization code grant error
response (Section 4.1.2.1), the implicit grant error response
(Section 4.2.2.1), or the token error response (Section 5.2), such
error codes MAY be defined.
Extension error codes MUST be registered (following the procedures in
Section 11.3) if the extension they are used in conjunction with is a
registered access token type, a registered endpoint parameter, or an
extension grant type. Error codes used with unregistered extensions
MAY be registered.
Error codes MUST conform to the error-code ABNF, and SHOULD be
prefixed by an identifying name when possible. For example, an error
identifying an invalid value set to the extension parameter "example"
should be named "example_invalid".
error-code = ALPHA *error-char
error-char = "-" / "." / "_" / DIGIT / ALPHA
9. Native Applications
[[ Pending consensus ]]
A native application is a client which is installed and executes on
the end-user's device (i.e. desktop application, native mobile
application). Native applications are often capable of interacting
with (or embedding) a user-agent but are limited in how such
interactions affects their overall end-user experience. In many
cases, native applications are incapable of receiving redirection
requests from the authorization server (e.g. due to firewall rules,
operating system restrictions).
Native applications can utilize OAuth in different ways, based on
their requirements and desired end-user experience:
o Use the authorization code grant type flow described in
Section 4.1 by launching an external user-agent. The native
application can capture the response by providing a redirection
URI identifying a local (non-network) resource (registered with
the operating system to invoke the native application as handler),
or by providing a redirection URI identifying a server-hosted
resource under the native application's control, which in turn
makes the response available to the native application (e.g. using
the user-agent window title or other locations accessible from
outside the user-agent).
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o Use the authorization code grant type flow described in
Section 4.1 by embedding a user-agent. The native application
obtains the response by directly communicating with the embedded
user-agent. Embedded user-agents are discouraged as they
typically provide a less consistent user experience and do not
enable the end-user to verify the authorization server's
authenticity.
Native applications SHOULD use the authorization code grant type flow
without client password credentials (due to their inability to keep
the credentials confidential) to obtain short-lived access tokens,
and use refresh tokens to maintain access.
When choosing between launching an external user-agent and an
embedding a user-agent, native application developers should consider
the following:
o External user-agents may improve completion rate as the end-user
may already have an active session with the authorization server
removing the need to re-authenticate, and provide a familiar user-
agent user experience. The end-user may also rely on extensions
or add-ons to assist with authentication (e.g. password managers
or 2-factor device reader).
o Embedded user-agents often offer a better end-user flow, as they
remove the need to switch context and open new windows but also
may provide less familiar features than the external user-agent.
o Embedded user-agents pose a security challenge because end-users
are authenticating in an unidentified window without access to the
visual protections offered by many user-agents. Embedded user-
agents educate end-user to trust unidentified requests for
authentication (making phishing attacks easier to execute).
10. Security Considerations
As a flexible and extensible framework, OAuth's security
considerations depend on many factors. The following sections
provide implementers with security guidelines focused on three common
client types:
Web Application
A web application is a client running on a web server. End-users
access the client via an HTML user interface rendered in a user-
agent on the end-user's device. The client credentials as well as
any access token issued to the client are stored on the web server
and are not exposed to or accessible by the end-user.
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User-Agent-based Application
A user-agent-based application is a client in which the client
code is downloaded from a web server and executes within a user-
agent on the end-user's device. The OAuth protocol data and
credentials are accessible to the end-user. Since such
applications directly reside within the user-agent, they can make
seamless use of the user-agent capabilities in the end-user
authorization process.
Native Application
A native application is a client which is installed and executes
on the end-user's device. The OAuth protocol data and credentials
are accessible to the end-user. It is assumed that such an
application can protect dynamically issued credentials, such as
refresh tokens, from eavesdropping by other applications residing
on the same device.
A comprehensive OAuth security model and analysis, as well as
background for the protocol design is provided in
[I-D.lodderstedt-oauth-security].
10.1. Client Authentication
The authorization server issues client credentials to web
applications for the purpose of authenticating them. The
authorization server is encouraged to consider using stronger client
authentication means than a client password. Application developers
MUST ensure confidentiality of client passwords and other
credentials.
The authorization server MUST NOT issue client passwords or other
credentials to native or user-agent-based applications for the
purpose of client authentication. The authorization server MAY issue
a client password or other credentials for a specific installation of
a native application on a specific device.
10.2. Client Impersonation
Given the inability of some clients to keep their client credentials
confidential, a malicious client can impersonate another client and
obtain access to protected resources. The authorization server MUST
authenticate the client whenever possible. If the authorization
server cannot authenticate the a client due to the client's
limitations, the authorization server should utilize other means to
protect resource owners from such malicious clients, including but
not limited to engaging the end-user to assist in identifying the
client and its source.
The authorization server SHOULD enforce explicit end-user
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authentication, or prompt the end-user to authorize access again,
providing the end-user with information about the client, scope, and
duration of the authorization. It is up to the end-user to review
the information in the context of the current client, and authorize
the request.
The authorization server SHOULD NOT automatically, without active
end-user interaction, process repeated authorization requests without
authenticating the client or relying on other measures to ensure the
repeated request comes from a valid client and not an impersonator.
The authorization server SHOULD require the client to pre-register
its redirection URI and validate the value of the "redirect_uri"
against the pre-registered value. The client MUST NOT serve an open
redirector resource which can be used by an attacker to construct an
URI that will pass the authorization server's redirection URI
matching rules, and will redirect the end-user's user-agent to the
attacker's server.
The authorization server SHOULD issue access tokens with limited
scope and duration to clients incapable of authenticating.
10.3. Access Token Credentials
Access token credentials MUST be kept confidential in transit and
storage, and shared only among the authorization server, the resource
servers the credentials are valid for, and the client to whom the
credentials were issued.
When using the implicit grant type, the access token credentials are
transmitted in the URI fragment, which can expose the credentials to
unauthorized parties.
The authorization server MUST ensure that access token credentials
cannot be generated, modified, or guessed to produce valid access
token credentials.
The client SHOULD request access token credentials with the minimal
scope and duration necessary. The authorization server SHOULD take
the client identity into account when choosing to honor the requested
scope, and MAY issue credentials with a lesser scope than requested.
10.4. Refresh Tokens
Authorization servers MAY issue refresh tokens to web and native
applications.
Refresh tokens MUST be kept confidential in transit and storage, and
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shared only among the authorization server and the client to whom the
refresh tokens were issued. The authorization server MUST maintain
the link between a refresh token and the client to whom it was
issued.
The authorization server MUST verify the link between the refresh
token and client identity whenever the client's identity can be
authenticated. When client authentication is not possible, the
authorization server SHOULD deploy other means to detect refresh
token abuse.
The authorization server MUST ensure that refresh tokens cannot be
generated, modified, or guessed to produce valid refresh tokens.
10.5. Request Confidentiality
Access token credentials, refresh tokens, resource owner passwords,
and client secrets MUST NOT be transmitted in the clear.
Authorization codes SHOULD NOT be transmitted in the clear.
10.6. Endpoints Authenticity
In order to prevent man-in-the-middle and phishing attacks, the
authorization server MUST implement and require TLS with server-side
authentication in all exchanges. The client MUST verify the
authorization server's TLS certificate, as well as the respective
certificate chain.
10.7. Credentials Guessing Attacks
The authorization server MUST prevent attackers from guessing access
tokens, authorization codes, refresh tokens, resource owner
passwords, and client secrets.
When generating tokens and other secrets not intended for direct
human utilization, the authorization server MUST use a reasonable
level of entropy in order to mitigate the risk of guessing attacks.
When creating secrets intended for human usage, the authorization
server MUST utilize other means to protect those secrets.
10.8. Phishing Attacks
Native applications SHOULD use external browsers instead of embedding
browsers within the application when requesting end-user
authorization. External browsers offer a familiar user experience
and a trusted environment in which end-users can confirm the
authenticity of the authorization server.
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To reduce the risk of phishing attacks, the authorization servers
MUST utilize TLS to allow user-agents to validate the authorization
server's identity. Service providers should educate their end-users
about the risks of phishing attacks and how they can verify the
authorization server's identity.
10.9. Authorization Codes
The transmission of authorization codes SHOULD be made over a secure
channel, and the client SHOULD implement TLS for use with its
redirection URI if the URI identifies a network resource.
Authorization codes MUST be kept confidential. Since authorization
codes are transmitted via user-agent redirections, they could
potentially be disclosed through user-agent history and HTTP referrer
headers.
Authorization codes operate as plaintext bearer credentials, used to
verify that the end-user who granted authorization at the
authorization server, is the same end-user returning to the client to
complete the process. Therefore, if the client relies on the
authorization code for its own end-user authentication, the client
redirection endpoint MUST require TLS.
Authorization codes SHOULD be short lived and MUST be single use. If
the authorization server observes multiple attempts to exchange an
authorization code for an access token, the authorization server
SHOULD revoke all access tokens already granted based on the
compromised authorization code.
If the client can be authenticated, the authorization servers MUST
authenticate the client and ensure that the authorization code was
issued to the same client.
10.10. Session Fixation
Session fixation attacks leverage the authorization code grant type,
by tricking an end-user to authorize access to a legitimate client,
but to a client account under the control of the attacker. The only
difference between a valid flow and the attack flow is in how the
victim reached the authorization server to grant access. Once at the
authorization server, the victim is prompted with a normal, valid
request on behalf of a legitimate and familiar client. The attacker
then uses the victim's authorization to gain access to the
information authorized by the victim.
In order to prevent such an attack, authorization servers MUST ensure
that the redirection URI used to obtain the authorization code, is
the same as the redirection URI provided when exchanging the
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authorization code for an access token. The authorization server
SHOULD require the client to pre-register their redirection URI and
if provided, MUST validate the redirection URI received in the
authorization request against the pre-registered value.
10.11. Redirection URI Validation
[[ Add specific recommendations about redirection validation and
matching ]]
10.12. Resource Owner Password Credentials
The resource owner password credentials grant type is often used for
legacy or migration reasons. It reduces the overall risk of storing
username and password in the client, but does not eliminate the need
to expose highly privileged credentials to the client.
This grant type carries a higher risk than the other grant types
because it maintains the password anti-pattern OAuth seeks to avoid.
The client could abuse the password or the password could
unintentionally be disclosed to an attacker (e.g. via log files or
other records kept by the client).
Additionally, because the resource owner does not have control over
the authorization process (the resource owner involvement ends when
it hands over its credentials to the client), the client can obtain
access tokens with a broader scope and longer duration than desired
by the resource owner. The authorization server SHOULD restrict the
scope and duration of access tokens issued via this grant type.
The authorization server and client SHOULD minimize use of this grant
type and utilize other grant types whenever possible.
10.13. XSRF/CSRF Prevention
[[ Add text with reference to the 'state' parameter ]]
11. IANA Considerations11.1. The OAuth Access Token Type Registry
This specification establishes the OAuth access token type registry.
Access token types are registered on the advice of one or more
Designated Experts (appointed by the IESG or their delegate), with a
Specification Required (using terminology from [RFC5226]). However,
to allow for the allocation of values prior to publication, the
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Designated Expert(s) may approve registration once they are satisfied
that such a specification will be published.
Registration requests should be sent to the [TBD]@ietf.org mailing
list for review and comment, with an appropriate subject (e.g.,
"Request for access toke type: example"). [[ Note to RFC-EDITOR: The
name of the mailing list should be determined in consultation with
the IESG and IANA. Suggested name: oauth-ext-review. ]]
Within at most 14 days of the request, the Designated Expert(s) will
either approve or deny the registration request, communicating this
decision to the review list and IANA. Denials should include an
explanation and, if applicable, suggestions as to how to make the
request successful.
Decisions (or lack thereof) made by the Designated Expert can be
first appealed to Application Area Directors (contactable using
app-ads@tools.ietf.org email address or directly by looking up their
email addresses on http://www.iesg.org/ website) and, if the
appellant is not satisfied with the response, to the full IESG (using
the iesg@iesg.org mailing list).
IANA should only accept registry updates from the Designated
Expert(s), and should direct all requests for registration to the
review mailing list.
11.1.1. Registration Template
Type name:
The name requested (e.g., "example").
Additional Token Endpoint Response Parameters:
Additional response parameters returned together with the
"access_token" parameter. New parameters MUST be separately
registered in the OAuth parameters registry as described by
Section 11.2.
HTTP Authentication Scheme(s):
The HTTP authentication scheme name(s), if any, used to
authenticate protected resources requests using access token of
this type.
Change controller:
For standards-track RFCs, state "IETF". For others, give the name
of the responsible party. Other details (e.g., postal address,
e-mail address, home page URI) may also be included.
Specification document(s):
Reference to document that specifies the parameter, preferably
including a URI that can be used to retrieve a copy of the
document. An indication of the relevant sections may also be
included, but is not required.
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This specification establishes the OAuth parameters registry.
Additional parameters for inclusion in the authorization endpoint
request, the authorization endpoint response, the token endpoint
request, or the token endpoint response, are registered on the advice
of one or more Designated Experts (appointed by the IESG or their
delegate), with a Specification Required (using terminology from
[RFC5226]). However, to allow for the allocation of values prior to
publication, the Designated Expert(s) may approve registration once
they are satisfied that such a specification will be published.
Registration requests should be sent to the [TBD]@ietf.org mailing
list for review and comment, with an appropriate subject (e.g.,
"Request for parameter: example"). [[ Note to RFC-EDITOR: The name of
the mailing list should be determined in consultation with the IESG
and IANA. Suggested name: oauth-ext-review. ]]
Within at most 14 days of the request, the Designated Expert(s) will
either approve or deny the registration request, communicating this
decision to the review list and IANA. Denials should include an
explanation and, if applicable, suggestions as to how to make the
request successful.
Decisions (or lack thereof) made by the Designated Expert can be
first appealed to Application Area Directors (contactable using
app-ads@tools.ietf.org email address or directly by looking up their
email addresses on http://www.iesg.org/ website) and, if the
appellant is not satisfied with the response, to the full IESG (using
the iesg@iesg.org mailing list).
IANA should only accept registry updates from the Designated
Expert(s), and should direct all requests for registration to the
review mailing list.
11.2.1. Registration Template
Parameter name:
The name requested (e.g., "example").
Parameter usage location:
The location(s) where parameter can be used. The possible
locations are: authorization request, authorization response,
token request, or token response.
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o Parameter usage location: token request, token response
o Change controller: IETF
o Specification document(s): [[ this document ]]
11.3. The OAuth Extensions Error Registry
This specification establishes the OAuth extensions error registry.
Additional error codes used together with other protocol extensions
(i.e. extension grant types, access token types, or extension
parameters) are registered on the advice of one or more Designated
Experts (appointed by the IESG or their delegate), with a
Specification Required (using terminology from [RFC5226]). However,
to allow for the allocation of values prior to publication, the
Designated Expert(s) may approve registration once they are satisfied
that such a specification will be published.
Registration requests should be sent to the [TBD]@ietf.org mailing
list for review and comment, with an appropriate subject (e.g.,
"Request for error code: example"). [[ Note to RFC-EDITOR: The name
of the mailing list should be determined in consultation with the
IESG and IANA. Suggested name: oauth-ext-review. ]]
Within at most 14 days of the request, the Designated Expert(s) will
either approve or deny the registration request, communicating this
decision to the review list and IANA. Denials should include an
explanation and, if applicable, suggestions as to how to make the
request successful.
Decisions (or lack thereof) made by the Designated Expert can be
first appealed to Application Area Directors (contactable using
app-ads@tools.ietf.org email address or directly by looking up their
email addresses on http://www.iesg.org/ website) and, if the
appellant is not satisfied with the response, to the full IESG (using
the iesg@iesg.org mailing list).
IANA should only accept registry updates from the Designated
Expert(s), and should direct all requests for registration to the
review mailing list.
11.3.1. Registration Template
Error name:
The name requested (e.g., "example").
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Error usage location:
The location(s) where the error can be used. The possible
locations are: authorization code grant error response
(Section 4.1.2.1), implicit grant error response
(Section 4.2.2.1), or token error response (Section 5.2).
Related protocol extension:
The name of the extension grant type, access token type, or
extension parameter, the error code is used in conjunction with.
Change controller:
For standards-track RFCs, state "IETF". For others, give the name
of the responsible party. Other details (e.g., postal address,
e-mail address, home page URI) may also be included.
Specification document(s):
Reference to document that specifies the error code, preferably
including a URI that can be used to retrieve a copy of the
document. An indication of the relevant sections may also be
included, but is not required.
12. Acknowledgements
The initial OAuth 2.0 protocol specification was edited by David
Recordon, based on two previous publications: the OAuth 1.0 community
specification [RFC5849], and OAuth WRAP (OAuth Web Resource
Authorization Profiles) [I-D.draft-hardt-oauth-01]. The Security
Considerations section was drafted by Torsten Lodderstedt, Mark
McGloin, Phil Hunt, and Anthony Nadalin.
The OAuth 1.0 community specification was edited by Eran Hammer-Lahav
and authored by Mark Atwood, Dirk Balfanz, Darren Bounds, Richard M.
Conlan, Blaine Cook, Leah Culver, Breno de Medeiros, Brian Eaton,
Kellan Elliott-McCrea, Larry Halff, Eran Hammer-Lahav, Ben Laurie,
Chris Messina, John Panzer, Sam Quigley, David Recordon, Eran
Sandler, Jonathan Sergent, Todd Sieling, Brian Slesinsky, and Andy
Smith.
The OAuth WRAP specification was edited by Dick Hardt and authored by
Brian Eaton, Yaron Goland, Dick Hardt, and Allen Tom.
This specification is the work of the OAuth Working Group which
includes dozens of active and dedicated participants. In particular,
the following individuals contributed ideas, feedback, and wording
which shaped and formed the final specification:
Michael Adams, Andrew Arnott, Dirk Balfanz, Scott Cantor, Blaine
Cook, Brian Campbell, Leah Culver, Bill de hOra, Brian Eaton, Brian
Ellin, Igor Faynberg, George Fletcher, Tim Freeman, Evan Gilbert,
Yaron Goland, Brent Goldman, Kristoffer Gronowski, Justin Hart, Craig
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Heath, Phil Hunt, Michael B. Jones, John Kemp, Mark Kent, Raffi
Krikorian, Chasen Le Hara, Rasmus Lerdorf, Torsten Lodderstedt, Hui-
Lan Lu, Paul Madsen, Alastair Mair, Eve Maler, James Manger, Mark
McGloin, Laurence Miao, Chuck Mortimore, Justin Richer, Peter Saint-
Andre, Nat Sakimura, Rob Sayre, Marius Scurtescu, Naitik Shah, Luke
Shepard, Vlad Skvortsov, Justin Smith, Jeremy Suriel, Christian
Stuebner, Paul Tarjan, Allen Tom, Franklin Tse, Nick Walker, Skylar
Woodward.
Appendix A. Editor's Notes
While many people contributed to this specification throughout its
long journey, the editor would like to acknowledge and thank a few
individuals for their outstanding and invaluable efforts leading up
to the publication of this specification. It is these individuals
without whom this work would not have existed, or reached its
successful conclusion.
David Recordon for continuously being one of OAuth's most valuable
assets, bringing pragmatism and urgency to the work, and helping
shape it from its very beginning, as well as being one of the best
collaborators I had the pleasure of working with.
Mark Nottingham for introducing OAuth to the IETF and setting the
community on this course. Lisa Dusseault for her support and
guidance as the Application area director. Blaine Cook, Peter Saint-
Andre, and Hannes Tschofenig for their work as working group chairs.
James Manger for his creative ideas and always insightful feedback.
Brian Campbell, Torsten Lodderstedt, Chuck Mortimore, Justin Richer,
Marius Scurtescu, and Luke Shepard for their continued participation
and valuable feedback.
Special thanks goes to Mike Curtis and Yahoo! for their unconditional
support of this work for over three years.
13. References13.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
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